Check the over all condition of the camera. Canon has had issues with inconsistent shutter life for years and years, though it seems they have gotten a better handle on it over the last 2 years.
So is a replaced shutter expected to last as long as a new? Longer? Are there adding internal parts other than the shutter I should be worried about? To me, a replaced shutter means the camera was probably heavily used, but in what setting...
I'd ask if it was mainly used for Video or Stills. I am shying away from anything that was mainly video use. That's a lot of heat on the sensor and makes me a little wary.